Synthetic resin sliding bearing

ABSTRACT

A synthetic resin-made sliding bearing ( 1 ) includes a synthetic resin-made lower casing ( 2 ), a synthetic resin-made upper casing ( 3 ) superposed on the lower casing ( 2 ), a synthetic resin-made disk-shaped thrust sliding bearing piece ( 4 ) disposed between the upper and the lower casings ( 3 ) and ( 2 ), and a synthetic resin-made cylindrical radial sliding bearing piece ( 5 ) disposed between the upper and the lower casings ( 3 ) and ( 2 ).

TECHNICAL FIELD

[0001] The present invention relates to a synthetic resin-made slidingbearing, and more particularly to a synthetic resin-made sliding bearingwhich is suitably incorporated in a strut-type suspension (Macphersontype) in a four-wheeled vehicle.

BACKGROUND ART

[0002] A strut-type suspension used in a front wheel of a four-wheeledvehicle generally has a structure in which a strut assemblyincorporating a hydraulic shock absorber in an outer cylinder formedintegrally with a main shaft is combined with a coil spring. In suchsuspensions, there is a type in which a piston rod of the strut assemblyrotates and a type in which the piston rod does not rotate when thestrut assembly rotates together with the coil spring on steeringoperation. In either type, there are cases where a synthetic resin-madesliding bearing in place of a rolling ball bearing is used between amounting member of a vehicle body and an upper spring seat of the coilspring so as to smoothly allow the rotation of the strut assembly.

[0003] The synthetic resin-made sliding bearing generally has asynthetic resin-made lower casing and a synthetic resin-made uppercasing superposed on the lower casing, and a sliding bearing piece or asliding bearing projection is disposed in a space between the lowercasing and the upper casing. However, if dust, muddy water, or the likeenters this space, there is a possibility that a desired bearingfunction cannot be obtained. Meanwhile, since the strut-type suspensionis fitted at a position where dust, rainwater, muddy water, or the likeis directly applied during the traveling of the vehicle, the workingenvironment of the sliding bearing fitted between the mounting member ofthe vehicle body and the upper spring seat of the coil spring becomesextremely severe. Accordingly, if the outer peripheral side and theinner peripheral side of the space where the sliding bearing piece orthe sliding bearing projection is disposed is directly open to theoutside, the risk of the entry of dust, rainwater, muddy water, or thelike from this opening into the space becomes very high, so that thesealing performance at this portion becomes extremely important. Inparticular, the aforementioned risk becomes increasingly high with thesynthetic resin-made sliding bearing in which the lower casing and theupper casing are formed with the inner peripheral side of the space opendownward so as to prevent the stagnation of water in the space.

[0004] The present invention has been devised in view of theabove-described aspects, and its object is to provide a syntheticresin-made sliding bearing which prevents the entry of dust, rainwater,muddy water, and the like onto sliding surfaces from the outerperipheral side and the inner peripheral side of the space where thesliding bearing piece is disposed, so as to eliminate a decline ofsliding characteristics attributable to the entry of the dust,rainwater, muddy water, and the like, thereby making it possible tomaintain smooth steering force at the time of the steering operation forextended periods of time.

DISCLOSURE OF INVENTION

[0005] A synthetic resin-made sliding bearing in accordance with a firstaspect of the invention comprises a synthetic resin-made lower casing, asynthetic resin-made upper casing superposed on the lower casing, asynthetic resin-made disk-shaped thrust sliding bearing piece disposedbetween the upper casing and the lower casing, and a syntheticresin-made cylindrical radial sliding bearing piece disposed between theupper casing and the lower casing, the lower casing including a tubularportion having an inner peripheral surface, a first annular plateportion formed integrally with an end portion of the tubular portion, afirst annular projection formed integrally with an upper surface of thefirst annular plate portion, an annular engaging projection formedintegrally with an outer edge of the first annular plate portion, asecond annular plate portion formed integrally with another end portionof the tubular portion, and a second annular projection formedintegrally with an upper surface of the second annular plate portion,the upper casing including a hollow cylindrical portion disposed insidethe tubular portion of the lower casing and having an inner peripheralsurface and an outer peripheral surface which are concentric with theinner peripheral surface of the tubular portion of the lower casing, athird annular plate portion formed integrally with an end portion of thehollow cylindrical portion, a first annular suspended portion formedintegrally with a lower surface of the third annular plate portion, anannular engaging suspended portion formed integrally with an outer edgeof the third annular plate portion, and a pair of concentric secondannular suspended portions formed integrally with another end portion ofthe hollow cylindrical portion, the first annular suspended portionbeing disposed in a first annular groove defined by the first annularprojection and the annular engaging projection, the annular engagingprojection being disposed in a second annular groove defined by thefirst annular suspended portion and the annular engaging suspendedportion, the second annular projection being disposed in a third annulargroove defined by the pair of second annular suspended portions, thethrust sliding bearing piece being disposed between the upper surface ofthe first annular plate portion and the lower surface of the thirdannular plate portion on an inner peripheral side of the first annularprojection in such a manner as to be slidably brought into contact withthe upper surface and the lower surface, and the radial sliding bearingpiece being disposed between the inner peripheral surface of the tubularportion and the outer peripheral surface of the hollow cylindricalportion in such a manner as to be slidably brought into contact with theinner peripheral surface of the tubular portion and the outer peripheralsurface of the hollow cylindrical portion.

[0006] According to the sliding bearing in accordance with the firstaspect, since the second annular projection is disposed in the thirdannular groove defined by the pair of second annular suspended portions,it is possible to prevent the entry of dust, rainwater, muddy water, andthe like onto the sliding surfaces of the radial sliding bearing piecefrom the inner peripheral side. Hence, it is possible to eliminate adecline of sliding characteristics attributable to the entry of thedust, rainwater, muddy water, and the like, thereby making it possibleto maintain smooth steering force at the time of the steering operationfor extended periods of time.

[0007] With the synthetic resin-made sliding bearing in accordance witha second aspect of the invention, in the sliding bearing according tothe first aspect, the first annular projection is formed integrally withthe upper surface of the first annular plate portion such that a topsurface thereof is higher than a top surface of the annular engagingprojection.

[0008] According to the sliding bearing in accordance with the secondaspect, since the top surface of the first annular projection is higherthan the top surface of the annular engaging projection, even ifrainwater, muddy water, or the like has ridden over the annular engagingprojection, the entry of such rainwater, muddy water, or the like ontothe sliding surfaces of the thrust sliding bearing piece can beprevented by the first annular projection. This makes it possible toeliminate the decline of sliding characteristics attributable to theentry of the rainwater, muddy water, and the like, thereby making itpossible to maintain smooth steering force at the time of the steeringoperation for extended periods of time.

[0009] With the synthetic resin-made sliding bearing in accordance witha third aspect of the invention, in the sliding bearing according to thefirst or second aspect, at least one of the inner peripheral surface ofthe tubular portion and the outer peripheral surface of the hollowcylindrical portion is formed with an annular stepped portion definingan annular step surface opposing an annular lower surface of the radialsliding bearing piece.

[0010] According to the sliding bearing in accordance with the thirdaspect, since the lowering of the radial sliding bearing piece can beprevented by the annular step surface, the radial sliding bearing piecebetween the inner peripheral surface of the tubular portion and theouter peripheral surface of the hollow cylindrical portion can be heldat a desired position.

[0011] With the synthetic resin-made sliding bearing in accordance witha fourth aspect of the invention, in the sliding bearing according tothe third aspect, the second annular projection is formed integrallywith the upper surface of the second annular plate portion such that atop surface thereof is lower than the annular step surface.

[0012] According to the sliding bearing in accordance with the fourthaspect, since the top surface of the second annular projection is lowerthan the annular step surface, even if rainwater, muddy water, or thelike has ridden over the second annular projection and entered betweenthe inner peripheral surface of the tubular portion and the outerperipheral surface of the hollow cylindrical portion, the level of suchrainwater, muddy water, or the like does not reach the annular stepsurface. Hence, it is possible to prevent the entry of such rainwater,muddy water, or the like onto the sliding surfaces of the thrust slidingbearing piece. This also makes it possible to eliminate the decline ofsliding characteristics attributable to the entry of the rainwater,muddy water, and the like, thereby making it possible to maintain smoothsteering force at the time of the steering operation for extendedperiods of time.

[0013] With the synthetic resin-made sliding bearing in accordance witha fifth aspect of the invention, in the sliding bearing according to anyone of the first to fourth aspects, the lower casing further includes athird annular projection formed integrally with the upper surface of thefirst annular plate portion, and the thrust sliding bearing piece isdisposed on an outer peripheral side of the third annular projection.

[0014] According to the sliding bearing in accordance with the fifthaspect, since the radial movement of the thrust sliding bearing piececan be prevented by the third annular projection, the thrust slidingbearing piece between the upper surface of the first annular plateportion and the lower surface of the third annular plate portion can beheld at a desired position.

[0015] With the synthetic resin-made sliding bearing in accordance witha sixth aspect of the invention, in the sliding bearing according to anyone of the first to fifth aspects, at least one of the inner peripheralsurface of the tubular portion and the outer peripheral surface of thehollow cylindrical portion is formed with another annular steppedportion defining another annular step surface opposing the annular uppersurface of the radial sliding bearing piece.

[0016] According to the sliding bearing in accordance with the sixthaspect, since the rise of the radial sliding bearing piece can beprevented by the other annular step surface, the radial sliding bearingpiece between the inner peripheral surface of the tubular portion andthe outer peripheral surface of the hollow cylindrical portion can beheld at a desired position.

[0017] The synthetic resin for forming the upper and lower casings inthe invention should preferably excel in sliding characteristics andmechanical characteristics including the wear resistance, shockresistance, and creep resistance. In addition, the synthetic resin forforming the thrust sliding bearing piece and the radial sliding bearingpiece which are accommodated between the upper and lower casings shouldpreferably have self-lubricity, in particular. For example, a polyacetalresin, a polyamide resin, a polyester resin such as polybutyleneterephthalate (PBT), and a polyolefin resin such as polyethylene andpolypropylene are suitably used. In addition, a polycarbonate resin orthe like may be used.

[0018] As material of the upper and lower casings, it is possible to usea synthetic resin similar to the synthetic resin for forming the thrustsliding bearing piece and the radial sliding bearing piece. Inparticular, however, a synthetic resin which gives a combinationexcelling in the frictional characteristics with the synthetic resinused for the thrust sliding bearing piece and the radial sliding bearingpiece and which has relatively high rigidity is desirable. To citedesirable combinations by way of example, as material of the thrustsliding bearing piece and the radial sliding bearing piece, on the onehand, and the upper and lower casings, on the other hand, it is possibleto cite the combination of polyacetal and polyimide, the combination ofpolyethylene and polyacetal, the combination of polyacetal and PBT, andthe combination of polyacetal and polyacetal.

[0019] In accordance with the invention, it is possible to provide asynthetic resin-made sliding bearing which prevents the entry of dust,rainwater, muddy water, and the like onto sliding surfaces from theouter peripheral side and the inner peripheral side of the space wherethe sliding bearing piece is disposed, so as to eliminate a decline ofsliding characteristics attributable to the entry of the dust,rainwater, muddy water, and the like, thereby making it possible tomaintain smooth steering force at the time of the steering operation forextended periods of time.

[0020] Hereafter, a detailed description will be given of the presentinvention with reference to the embodiments shown in the drawings. Itshould be noted that the present invention is not limited to theseembodiments.

BRIEF DESCRIPTION OF DRAWINGS

[0021]FIG. 1 is a cross-sectional view of a preferred embodiment of theinvention;

[0022]FIG. 2 is a partial enlarged cross-sectional view of theembodiment shown in FIG. 1;

[0023]FIG. 3 is a plan view of a thrust sliding bearing piece of theembodiment shown in FIG. 1;

[0024]FIG. 4 is a perspective view of a radial sliding bearing piece ofthe embodiment shown in FIG. 1; and

[0025]FIG. 5 is an explanatory cross-sectional view of an example inwhich the embodiment shown in FIG. 1 is used in a strut assembly.

EMBODIMENTS

[0026] In FIGS. 1 to 4, a synthetic resin-made sliding bearing 1 inaccordance with this embodiment is comprised of a synthetic resin-madelower casing 2, a synthetic resin-made upper casing 3 superposed on thelower casing 2, a synthetic resin-made disk-shaped thrust slidingbearing piece 4 disposed between the upper and lower casings 3 and 2,and a synthetic resin-made cylindrical radial sliding bearing piece 5disposed between the upper and lower casings 3 and 2.

[0027] The lower casing 2 includes a tubular portion 12 having an innerperipheral surface 11, an annular plate portion 13 formed integrallywith an end portion of the tubular portion 12, an annular projection 15formed integrally with an outer side of an upper surface 14 of theannular plate portion 13, an annular projection 16 formed integrallywith an inner side of the upper surface 14 of the annular plate portion13, an annular engaging projection 17 formed integrally with an outeredge of the annular plate portion 13, an annular plate portion 18 formedintegrally with the other end portion of the tubular portion 12, and anannular projection 20 formed integrally with an upper surface 19 of theannular plate portion 18.

[0028] The tubular portion 12 consists of an hollow cylindrical portion25 having a cylindrical inner peripheral surface 24 which is a portionof the inner peripheral surface 11, as well as a conical tubular portion27 formed integrally with the hollow cylindrical portion 25 and having aconical inner peripheral surface 26 which is another portion of theinner peripheral surface 11. The annular projection 15 is formedintegrally with the upper surface 14 of the annular plate portion 13such that its top surface 28 is δ1 higher than a top surface 29 of theannular engaging projection 17. The annular engaging projection 17 hasin its substantially central portion an annular enlarged portion 30extending outwardly and has on an outer surface of the enlarged portion30 an annular inclined engaging surface 31.

[0029] The upper casing 3 includes a hollow cylindrical portion 37disposed inside the tubular portion 12 and having an inner peripheralsurface 35 and an outer peripheral surface 36 which are concentric withthe inner peripheral surface 24 of the hollow cylindrical portion 25; anannular plate portion 38 formed integrally with an end portion of thehollow cylindrical portion 37; an annular suspended portion 40 formedintegrally with an outer side of a lower surface 39 of the annular plateportion 38; an annular engaging suspended portion 41 formed integrallywith an outer edge of the annular plate portion 38; and a pair ofconcentric annular suspended portions 42 and 43 formed integrally withthe other end portion of the hollow cylindrical portion 37.

[0030] The annular engaging suspended portion 41 has in its lowerportion an enlarged portion 45 extending inwardly and has on an innersurface of the enlarged portion 45 an annular inclined engaging surface46, and the inclined engaging surface 46 is opposed to the inclinedengaging surface 31. An annular stepped portion 49 defining an annularstep surface 48 opposing an annular lower surface 47 of the radialsliding bearing piece 5 is formed on at least one of the innerperipheral surface 11 of the tubular portion 12 and the outer peripheralsurface 36 of the hollow cylindrical portion 37, i.e., on the innerperipheral surface 11 of the tubular portion 12 in this embodiment. Theinner peripheral surface 24 and the inner peripheral surface 26 areconnected to each other via the annular step surface 48. An annularstepped portion 52 defining an annular step surface 51 opposing anannular upper surface 50 of the radial sliding bearing piece 5 is formedon at least one of the inner peripheral surface 11 of the tubularportion 12 and the outer peripheral surface 36 of the hollow cylindricalportion 37, i.e., on the outer peripheral surface 36 of the hollowcylindrical portion 37 in this embodiment. The annular projection 20 isformed integrally with the upper surface 19 of the annular plate portion18 such that its top surface 53 is δ2 lower than the annular stepsurface 48.

[0031] The annular suspended portion 40 is disposed in an annular groove61 defined by the annular projection 15 and the annular engagingprojection 17, the annular engaging projection 17 is disposed in anannular groove 62 defined by the annular suspended portion 40 and theannular engaging suspended portion 41, and the annular projection 20 isdisposed in an annular groove 63 defined by the pair of annularsuspended portions 42 and 43.

[0032] The thrust sliding bearing piece 4 is disposed between the uppersurface 14 of the annular plate portion 13 and the lower surface 39 ofthe annular plate portion 38 on the inner peripheral side of the annularprojection 15 and the outer peripheral side of the annular projection 16in such a manner as to be slidably brought into contact with the uppersurface 14 and the lower surface 39. In the thrust sliding bearing piece4 having an annular lower surface 71 and an annular upper surface 72which are slidably brought into contact with the upper surface 14 andthe lower surface 39, respectively, a plurality of grooves 73 and 74extending in the radial direction for storing grease (a lubricating oil)are formed at equal intervals in the circumferential direction in thelower surface 71 and the upper surface 72, respectively.

[0033] The radial sliding bearing piece 5 is disposed between the innerperipheral surface 24 of the hollow cylindrical portion 25 and the outerperipheral surface 36 of the hollow cylindrical portion 37 in such amanner as to be slidably brought into contact with the inner peripheralsurface 24 and the outer peripheral surface 36. In the radial slidingbearing piece 5 having an outer peripheral surface 75 and an innerperipheral surface 76 which are slidably brought into contact with theinner peripheral surface 24 and the outer peripheral surface 36,respectively, a plurality of grooves 77 extending in the axial directionfor storing grease (lubricating oil) are formed at equal intervals inthe circumferential direction in the inner peripheral surface 76.

[0034] As shown in FIG. 5, in a state in which, after a piston rod 81 ofa shock absorber in a strut assembly is passed through an insertion holedefined by the inner peripheral surface 35 of the sliding bearing 1, anannular upper surface 83 of the upper casing 3 is made to closely abutagainst a mounting member 82 on a vehicle side where one end of thepiston rod 81 is attached, while an annular lower surface 84 of thelower casing 2 is made to closely abut against an upper spring seat 86for a coil spring 85 in the strut assembly, the above-describedsynthetic resin-made sliding bearing 1 is fitted between the upperspring seat 86 and the mounting member 82 so as to be used. At thistime, the inner peripheral surface 35 is made to closely abut againstthe outer peripheral surface of a hollow cylindrical portion 87 of themounting member 82.

[0035] When the strut assembly is rotated by the steering operation, thelower casing 2 is rotated with respect to the upper casing 3, thisrotation of the lower casing 2 is made smooth by the thrust slidingbearing 4 and the radial sliding bearing 5 which are disposed betweenthe upper and lower casings 3 and 2. Accordingly, the steering operationis also effected without resistance. In addition, the entry of dust andthe like into a space 91 between the upper and lower casings 3 and 2 isprevented on the inner peripheral side by a labyrinth formed by theannular projection 20 and the annular suspended portions 42 and 43 andon the outer peripheral side by a labyrinth formed by the annularprojection 15 and the annular engaging projection 17 as well as theannular suspended portion 40 and the annular engaging suspended portion41. Thus it is possible to reliably prevent the entry of dust and thelike onto the respective sliding surfaces of the thrust sliding bearingpiece 4 and the radial sliding bearing piece 5 which are disposedbetween these two labyrinths.

[0036] According to the sliding bearing 1, since the annular projection20 is disposed in the groove 63 defined by the pair of annular suspendedportions 42 and 43, it is possible to prevent the entry of dust,rainwater, muddy water, and the like onto the outer and inner peripheralsurfaces 75 and 76, which are the sliding surfaces of the radial slidingbearing piece 5, from the inner peripheral side. Hence, it is possibleto eliminate a decline of sliding characteristics attributable to theentry of the dust, rainwater, muddy water, and the like, thereby makingit possible to maintain smooth steering force at the time of thesteering operation for extended periods of time.

[0037] In addition, according to the sliding bearing 1, since the topsurface 28 of the annular projection 15 is δ1 higher than the topsurface 29 of the annular engaging projection 17, even if rainwater,muddy water, or the like has ridden over the annular engaging projection17, the entry of such rainwater, muddy water, or the like onto the lowersurface 71 and the upper surface 72, which are the sliding surfaces ofthe thrust sliding bearing piece 4, can be prevented by the annularprojection 15. This makes it possible to eliminate the decline ofsliding characteristics attributable to the entry of the rainwater,muddy water, and the like, thereby making it possible to maintain smoothsteering force at the time of the steering operation for extendedperiods of time. Additionally, the lowering of the radial slidingbearing piece 5 can be prevented by the annular step surface 48, so thatthe radial sliding bearing piece 5 between the inner peripheral surface11 of the tubular portion 12 and the outer peripheral surface 36 of thehollow cylindrical portion 37 can be held at a desired position. Sincethe top surface 53 of the annular projection 20 is δ2 lower than theannular step surface 48, even if rainwater, muddy water, or the like hasridden over the annular projection 20, the level of such rainwater,muddy water, or the like does not reach the annular step surface 48.Hence, it is possible to prevent the entry of such rainwater, muddywater, or the like onto the sliding surfaces of the radial slidingbearing piece 5. This also makes it possible to eliminate the decline ofsliding characteristics attributable to the entry of the rainwater,muddy water, and the like, thereby making it possible to maintain smoothsteering force at the time of the steering operation for extendedperiods of time. Furthermore, the radial movement of the thrust slidingbearing piece 4 can be prevented by the annular projection 16, so thatthe thrust sliding bearing piece 4 between the upper surface 14 of theannular plate portion 13 and the lower surface 39 of the annular plateportion 38 can be held at a desired position. In addition, the rise ofthe radial sliding bearing piece 5 can be prevented by the annular stepsurface 51, so that the radial sliding bearing piece 5 between the innerperipheral surface 11 of the tubular portion 12 and the outer peripheralsurface 36 of the hollow cylindrical portion 37 can be held at a desiredposition.

[0038] It should be noted that the inclined engaging surface 31 and theinclined engaging surface 46 opposing each other may be resilientlybrought into contact with each other by the resiliency of the annularengaging projection 17 and the annular engaging suspended portion 41,and a resiliently sealing means may be formed in addition to the sealingmeans using the labyrinth. Still alternatively, the inclined engagingsurface 31 and the inclined engaging surface 46 may be opposed to eachother with a very small gap therebetween. In addition, although thegroove 77 is provided in the inner peripheral surface 76, the groove 77may be provided in the outer peripheral surface 75 in conjunction withit or in place of it.

1. A synthetic resin-made sliding bearing, comprising: a syntheticresin-made lower casing, a synthetic resin-made upper casing superposedon said lower casing, a synthetic resin-made disk-shaped thrust slidingbearing piece disposed between said upper casing and said lower casing,and a synthetic resin-made cylindrical radial sliding bearing piecedisposed between said upper casing and said lower casing, said lowercasing including a tubular portion having an inner peripheral surface, afirst annular plate portion formed integrally with an end portion ofsaid tubular portion, a first annular projection formed integrally withan upper surface of said first annular plate portion, an annularengaging projection formed integrally with an outer edge of said firstannular plate portion, a second annular plate portion formed integrallywith another end portion of said tubular portion, and a second annularprojection formed integrally with an upper surface of said secondannular plate portion, said upper casing including a hollow cylindricalportion disposed inside said tubular portion of said lower casing andhaving an inner peripheral surface and an outer peripheral surface whichare concentric with the inner peripheral surface of said tubular portionof said lower casing, a third annular plate portion formed integrallywith an end portion of said hollow cylindrical portion, a first annularsuspended portion formed integrally with a lower surface of said thirdannular plate portion, an annular engaging suspended portion formedintegrally with an outer edge of said third annular plate portion, and apair of concentric second annular suspended portions formed integrallywith another end portion of said hollow cylindrical portion, said firstannular suspended portion being disposed in a first annular groovedefined by said first annular projection and said annular engagingprojection, said annular engaging projection being disposed in a secondannular groove defined by said first annular suspended portion and saidannular engaging suspended portion, said second annular projection beingdisposed in a third annular groove defined by said pair of secondannular suspended portions, said thrust sliding bearing piece beingdisposed between the upper surface of said first annular plate portionand the lower surface of said third annular plate portion on an innerperipheral side of said first annular projection in such a manner as tobe slidably brought into contact with the upper surface and the lowersurface, and said radial sliding bearing piece being disposed betweenthe inner peripheral surface of said tubular portion and the outerperipheral surface of said hollow cylindrical portion in such a manneras to be slidably brought into contact with the inner peripheral surfaceof said tubular portion and the outer peripheral surface of said hollowcylindrical portion.
 2. The synthetic resin-made sliding bearingaccording to claim 1, wherein said first annular projection is formedintegrally with the upper surface of said first annular plate portionsuch that a top surface thereof is higher than a top surface of saidannular engaging projection.
 3. The synthetic resin-made sliding bearingaccording to claim 1 or 2, wherein at least one of the inner peripheralsurface of said tubular portion and the outer peripheral surface of saidhollow cylindrical portion is formed with an annular stepped portiondefining an annular step surface opposing an annular lower surface ofsaid radial sliding bearing piece.
 4. The synthetic resin-made slidingbearing according to claim 3, wherein said second annular projection isformed integrally with the upper surface of said second annular plateportion such that a top surface thereof is lower than the annular stepsurface.
 5. The synthetic resin-made sliding bearing according to anyone of claims 1 to 4, wherein said lower casing further includes a thirdannular projection formed integrally with the upper surface of saidfirst annular plate portion, and said thrust sliding bearing piece isdisposed on an outer peripheral side of said third annular projection.6. The synthetic resin-made sliding bearing according to any one ofclaims 1 to 5, wherein at least one of the inner peripheral surface ofsaid tubular portion and the outer peripheral surface of said hollowcylindrical portion is formed with another annular stepped portiondefining another annular step surface opposing the annular upper surfaceof said radial sliding bearing piece.